Fast turn-off circuit arrangement

ABSTRACT

A circuit arrangement having at least one electric main switch (T 1 ) with a reference electrode (E), a control electrode (B), and a work electrode (C). A recovery diode (D 1;  D 2 ) is connected antiparallel to the main flow direction of each main switch (T 1 ). In order to speed up the switch-off process and in particular to reduce the attendant power loss, each main switch (T 1 ) is assigned an electric auxiliary switch (T 11;  T 22 ), whose work electrode is connected to the control electrode (B) of the associated main switch (T 1 ) and whose reference electrode is connected to the reference electrode (E) of the associated main switch (T 1 ). The capacitor (C 11 ) is disposed between the control electrode of the auxiliary switch (T 11;  T 22 ) and the work electrode (C) of the associated main switch (T 1 ). A discharge unit (D 11 ) is disposed between the control electrode and the reference electrode of the auxiliary switch in such a way that the capacitor (C 11 ) can be discharged during the transition of the main switch (T 1 ) from the OFF state to the ON state.

FIELD OF THE INVENTION

The present invention relates to a circuit arrangement, having at leastone electric main switch with a reference electrode, a control electrodeand a work electrode, and a free-wheeling diode which is connectedantiparallel to the main flow direction of each main switch.

In electronics in general but especially in power electronics, there isa need to be able to process the highest possible power levels whileoccupying the least possible space. This is associated with the demandfor keeping incident power losses minimal, since a power loss isconverted into heat and as a result, (larger) cooling bodies and hencelarger housing dimensions are needed. In externally-controlled andself-controlled transistor inverters, for instance, the incident powerloss is less, the higher the speed and resolution with which theswitching events of the transistors proceed. Particularly when bipolarswitching transistors are used, it is especially difficult to achievebrief switching events. Although the invention is applicable to circuitswith field effect transistors, the problems and their solution accordingto the invention will be described below taking bipolar transistors asan example.

BACKGROUND OF THE INVENTION

The problems the invention seeks to solve will first be presented withreference to FIG. 1a. FIG. 1a shows the standard situation, known fromthe prior art, of a power switching transistor T1, in this case abipolar transistor, to which a free-wheeling diode D1 is connectedanti-parallel. The three externally accessible terminals of thetransistor are marked C for collector (work electrode), B for base(control electrode), and E for emitter (reference electrode). Let U_(CE)be the voltage that drops between the collector and the emitter, U_(BE)be the voltage that drops between the base and the emitter, I_(C) be thecurrent flowing into the collector, and I_(B) be the current flowinginto the base. Between the collector and the base, there is a parasiticcapacitance, the so-called Miller capacitance C_(CB). This iscorrespondingly true for field effect transistors as well. Thedefinitive power loss during a switching event is determined by theproduct I_(C)·U_(CE). In FIG. 1b, the course of not only these twovariables but also the course of the base-to-emitter voltage U_(BE) andof the base current I_(B) are plotted over time. A relatively loss-freeand thus desirable switching event is characterized in that as soon asU_(CE) begins to rise, the collector current I_(C) drops sharply. Thecourse over time of the variables I_(C) and U_(CE), shown for thecircuit in FIGS. 1a and 1 b, does not meet this condition, for thefollowing reasons: First, for the discussion below it will be assumedthat the emitter of the transistor T1 is connected to ground. Thus ifthe voltage at the collector increases, that is, if U_(CE) rises, thenbecause of the charge current through the Miller capacitance C_(CB) andbecause of the voltage-related “softness” of the base terminal, the basevoltage U_(BE) is “slaved”; that is, U_(BE) also increases (see thecircle in FIG. 1b) instead of decreasing. Since the base triggering hasa so-called current source characteristic, the current that charges theMiller capacitance C_(CB) acts with negative feedback on the baseelectrode of the transistor T1. The switch-off event is slowed downsharply as a result: While U_(CE) is already rising, I_(C) is stillpresent in virtually its full intensity. This also becomes clear fromthe convex course of the curve of the current I_(C) during theswitch-off event. The shaded area marked A corresponds to the chargethat still flows through the transistor even though the transistor hasalready been “switched off”. The course of the current I_(L) through anohmic-inductive load, which is connected to the work electrode of themain switch, is indicated by dashed lines. The charge for the chargereversal event, marked by the area B, is accordingly furnished bytransistor capacitors (not shown). The ratio of area A to area B, thatis, of the switch-off current to the charge reversal current, can beconsidered a measure for the losses of the switchover event. The lowerthe ratio of A to B is, the less are the losses that occur in aswitchover event.

Previous ways of speeding up such switch-off events provided on the onehand connecting a resistor, on an order of magnitude of less than 100Ω,parallel to the base-to-emitter path, and on the other connecting aseries circuit comprising a capacitor with a capacitance of ≦10 nF and abe resistance of ≦100Ω parallel to the base-to-emitter path. The resultsof these versions are unsatisfactory, however, because the switch-offlosses are still great, as they were before.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is therefore to refine a circuitarrangement of the type defined at the outset such that the lossesoccurring in a switch-off event of the main switch are as slight aspossible.

For attaining this object, the invention provides that each main switchis assigned an electric auxiliary switch, whose work electrode isconnected to the control electrode of the associated main switch andwhose reference electrode is connected to the reference electrode of theassociated main switch, and at least one capacitor is disposed betweenthe control electrode of the auxiliary switch and the work electrode ofthe associated main switch, and a discharge unit is disposed between thecontrol electrode and the reference electrode of the auxiliary switch insuch a way that the at least one capacitor can be discharged during thetransition of the main switch from the OFF state to the ON state.

The embodiment according to the invention makes use of the recognitionthat a voltage increase at the work electrode of the main switch can betransmitted to the control electrode of the auxiliary switch via acapacitor. Given a suitable choice of the auxiliary switch, the chargingevent of the capacitor trips the transition of the switch to the ONstate. Since the work electrode of the auxiliary switch is connected tothe control electrode of the main switch, active charge carriers arethereby drawn from the control electrode of the main switch. Theinfluence of the Miller capacitance C_(CB), which slows down theswitch-off event of the main switch, can be counteracted as a result.This leads to a marked speeding up of the switch-off event and thus tomarkedly lesser losses than in the versions of the prior art. Thedischarge unit serves to discharge the capacitor between the switch-offevents, so that it is again available for the ensuing switch-off eventor in other words can be charged again.

In its simplest embodiment, the discharge unit comprises a singleresistor. In an alternative embodiment, the discharge unit can include adischarge diode, preferably in the form of a Schottky diode, Zener diodeor p-n diode; at least one resistor can be connected in series withand/or parallel to the discharge diode. The discharge unit can have aswitch-off input terminal, by way of which a signal that switches theauxiliary switch to the ON state can be applied. The connection of theswitch-off input terminal to the control electrode of the auxiliaryswitch preferably includes a shut-down diode, which with respect to thecontrol electrode of the auxiliary switch is oriented like the dischargediode. The switch-off diode can be embodied as a p-n or Schottky diode.

The discharge unit can have a sense output terminal, which is connectedto the control electrode of the auxiliary switch such that the switchingstatus of the main switch and/or the auxiliary switch can beinterrogated via the sense output terminal. At least one capacitor forshifting the potential can be disposed between the sense output terminaland the control electrode of the auxiliary switch.

The circuit arrangement of the invention can also have an antisaturationunit, which is disposed between the work electrode and the controlelectrode of the auxiliary switch and which prevents saturation of thecontrol electrode of the auxiliary switch. In its simplest embodiment,the antisaturation unit can be embodied by a single resistor, which isdisposed such that in the event of saturation of the control electrodeof the auxiliary switch, charge carriers can flow away to the workelectrode of the auxiliary switch. In an alternative, especiallypreferred embodiment, the antisaturation unit can have an antisaturationdiode, which is disposed such that it performs the same purpose. Theantisaturation diode can be a p-n or Schottky diode; at least oneresistor can be connected in series with and/or parallel to theantisaturation diode.

A main switch can be a bipolar transistor, but it can also be realizedwith the associated free-wheeling diode by a MOSFET. As the auxiliaryswitch, the following can be considered: a bipolar transistor, a bipolartransistor with a series diode in the collector, a MOSFET, or a MOSFETwith a series diode in the drain, and if a series diode is used, itsorientation is made such that a current flow in the main flow directionof the associated auxiliary switch is made possible. This series diodeis preferably in the form of a Schottky diode.

The invention also includes a bridge circuit having at least one firstand one second circuit arrangement, in which a bridge is formed byconnecting the reference electrode of the main switch of the second(“upper”) circuit arrangement to the work electrode of the main switchof the first (“lower”) circuit arrangement, optionally with theinterposition of additional components. A bridge circuit of this kindcan be part of a free-running oscillator circuit for operating a load,which furthermore has a switching control device for feedback of theload current to the control electrodes of the main switches of the firstand second circuit arrangements, and the control electrode of each mainswitch is connected by a respective terminal line to the switchingcontrol device, and the two terminal lines are connected in turn to oneanother via at least one so-called base bridge capacitor. The switchingcontrol device can be a control transformer. The base bridge capacitorcan be connected directly to the control electrode of each main switchand/or directly to the output of the switching control device orientedtoward the control electrode of the applicable main switch.

Other advantageous refinements can be learned from the dependent claims.

Exemplary embodiments will be described in further detail below inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows the wiring of a power transistor with a free-wheelingdiode, of the kind known from the prior art, for defining some variablesas an initial situation;

FIG. 1b shows the courses over time of the collector current I_(C), thecollector-to-emitter voltage U_(CE), the base-to-emitter voltage U_(BE),and the base current I_(B) for a switch-off event of the powertransistor of FIG. 1a;

FIG. 2a shows a very simple embodiment of a circuit arrangementaccording to the invention;

FIG. 2b shows the courses over time of the collector current I_(C), thecollector-to-emitter voltage U_(CE), the base-to-emitter voltage U_(BE),and the base current I_(B) for a switch-off event of the circuitarrangement of FIG. 2a;

FIG. 2c shows a variation of the embodiment depicted in FIG. 2a with onetype of discharge unit;

FIGS. 2d to 2 f are variations of the discharge unit shown in FIG. 2c;

FIG. 3 shows a basic circuit diagram for circuit arrangements accordingto the invention;

FIG. 4 shows an example of a circuit for the discharge unit;

FIG. 5 shows an example of a circuit with two circuit arrangements ofthe invention, used by way of example in an inverter;

FIGS. 5a to 5 c are different embodiments of the circuit shown in FIG.5;

FIG. 6 shows the course over time of various variables of the exemplarycircuit of FIG. 5;

FIGS. 7a to 7 e are different embodiments of the circuit shown in FIG.3; and

FIGS. 8a to 8 d are variations of the antisaturation unit of FIG. 3.

DETAILED DESCRIPTION

FIG. 2a shows the circuit arrangement of FIG. 1a, augmented according tothe present invention; for the discussion below, with reference totransistor T1, let its collector be its work electrode, its base be itscontrol electrode and its emitter be its reference electrode, and withreference to transistor T11, let its collector be its work electrode,its base be its control electrode and its emitter be its referenceelectrode; as its auxiliary switch, the transistor T1 is assigned thetransistor T11, whose work electrode is connected to the controlelectrode of transistor T1. The emitter of transistor T11 is connectedto the reference electrode of transistor T1. The control electrode oftransistor T11 is connected on the one hand to the work electrode oftransistor T1 via a capacitor C11, and on the other to the referenceelectrodes of both transistors via a discharge diode D11.

The function of the circuit arrangement of FIG. 2a: as soon as U_(CE)begins to rise, the base of the auxiliary transistor T11 experiences theflow of current that charges the positive feedback capacitor C11. Thisturns on the auxiliary transistor T11, thus connecting the base of themain transistor T1 to the emitter of the auxiliary transistor T11 withlow resistance. As a result, charge carriers can flow out of thecollector-to-base transition of the main transistor T1, via theauxiliary transistor T11.

With reference to FIG. 2, it is clear that this wiring provision leadsto a markedly lower-loss switch-off event than the circuit arrangementof FIG. 1a: The outflow of charge carriers from the collector-to-basetransition of T1 can be documented in FIG. 2b at the negative peak inthe course of the base current I_(B), precisely at the point whereU_(CE) begins to rise. At the same instant, the base-to-emitter voltagebecomes nearly 0 volts (circle in FIG. 2b). The two provisions together,that is, the outflow of charge carriers from the base of the maintransistor T1 and clamping of the base-to-emitter voltage U_(BE) of themain transistor T1 near 0 volts, leads to a marked acceleration of theswitch-off event. Compared to the switch-off event of FIG. 1b, the curvecourse of the collector current I_(C) is now concave. The current I_(C)has already reverted to acceptable values, as long as thecollector-to-emitter voltage U_(CE) is still low. The ratio of the areaA′ to the area B′ has become substantially smaller, which is anindicator of markedly lower losses during the switch-off event.

FIG. 3 shows a basic circuit diagram of a circuit arrangement 10 of theinvention. Of the terminals shown on the right in the drawing, terminal1 designates the work electrode of the main switch T1; terminal 2designates the control electrode of the main switch T1 and the workelectrode of the auxiliary switch T11; terminal 3 designates the controlelectrode of the auxiliary switch T11; terminal 4 designates a shut-downinput terminal of the discharge unit E11; terminal 5 designates a senseoutput terminal of the discharge unit E11; and terminal 6 designates thereference electrode for both the main switch T1 and the auxiliary switchT11. A free-wheeling diode D1 is connected anti-parallel to the mainswitch T1. The positive feedback capacitor C11 is, as already mentioned,disposed between the work electrode of the main switch T1 and thecontrol electrode of the auxiliary switch T11. The discharge unit E11 isdisposed between the control electrode of the auxiliary switch T11 andthe reference electrode of both switches. An antisaturation circuit A11,which is described in further detail below, can be provided between thecontrol electrode of the main switch or the work electrode of theauxiliary switch and the control electrode of the auxiliary switch.

The main switch T1 can be embodied as a bipolar transistor; thecombination of a main switch T1 and a recovery diode D1 can also beembodied by a MOSFET, in which the body diode of the MOSFET takes on thefunction of the free-wheeling diode D1.

The auxiliary switch T11 can be a bipolar transistor, a bipolartransistor with a series diode in the collector, a MOSFET, or a MOSFETwith a series diode in the drain, and if a series diode is used, itsorientation is made such that a current flow in the main flow directionof the associated auxiliary switch T11 is made possible. This seriesdiode of the auxiliary switch T11 can be a p-n diode or preferably aSchottky diode. A simple embodiment of the discharge unit E11 hasalready been presented in conjunction with FIG. 2a. It can be in theform of a Schottky diode, Zener diode, or p-n diode. Its function is toenable a discharge of the capacitor C11 before the next time the mainswitch T1 is turned off.

FIG. 4 shows a further embodiment of the discharge unit E11. In thisembodiment, a shut-down input terminal SD is connected via a diodeD_(SD) to the output of the discharge unit that is to be connected tothe control electrode of the auxiliary switch T11. The switch-off diodeD_(SD) can be embodied as a p-n or Schottky diode. Via the switch-offinput SD, the auxiliary switch T11 can be turned on from outside. As aresult, the triggering of the main switch T1 is short-circuited. Thisenables the use of the switch-off input for safety shutoff, for instanceif a component of this circuit becomes saturated or the circuit becomestoo hot. The diode D_(SD) prevents the positive feedback function of thepositive feedback capacitor C11 from being attenuated by the shut-offinput terminal SD, as would be the case if charge carriers did not, asintended, flow out to the control electrode of the auxiliary switch T11but instead flowed out of the shut-off input terminal.

The discharge unit E11 of FIG. 4 also has a sense output terminal, withwhich the status of the discharge unit and thus the switching status ofthe main switch and/or the auxiliary switch can be interrogated. Acapacitor C_(S11) can be provided, in order to shift the potential ofthe sense output terminal to the desired level. The sense outputterminal can advantageously be employed especially in soft switching andin externally controlled half bridges.

The circuit arrangement of the invention can be employed in many kindsof circuits, such as step-down converters, step-up converters,buck-boost converters, power factor correction circuits, Ćuk converters,etc., including especially operating equipment for electric lamps. As anexample, FIG. 5 shows the use of two circuit arrangements of theinvention in a self-controlled or in other words self-oscillatinginverter for operating a low-voltage halogen incandescent lamp. Theinverter includes a first and a second circuit arrangement 10 a and 10 baccording to the invention. Each of these circuit arrangements includesone main switch T1, T2, one auxiliary switch T11, T22, one free-wheelingdiode D1, D2, one discharge diode D11, D22, and one positive feedbackcapacitor C11, C22. A so-called base bridge capacitor C_(BB) (optional)is connected between the control electrodes of the two main switches T1,T2, and it serves as it were to “draw away” the possibly prematurelyensuing current for opening the base or turning on the transistor.Details about the base bridge capacitor can be learned from GermanPatent Disclosure DE 197 28 295 A1 (whose inventor is the same as thatof the present invention), and this disclosure is incorporated herein byreference. The two auxiliary transistors T11 and T22 have the furtheradvantage that in principle they cancel out the slowing effect of thebase bridge capacitor on the switch-off process. For triggering the twomain switches, a control transformer STR is used, through whose primarywinding the current I_(MP) flows and whose secondary windings areconnected to the control inputs of the two main switches T1 and T2. Theload is embodied here by a lamp that is coupled by a transformer; thewinding of the transformer through which the current I_(MP) flows isconnected on the one hand to the primary winding of the controltransformer STR and on the other to coupling capacitors C_(K1) andC_(K2). The coupling capacitor C_(K2) is connected to the work electrodeof the transistor T2, and the coupling capacitor C_(K1) is coupled tothe reference electrode of the transistor T1. The function of the rodcore choke L is of no significance to understanding the presentinvention; details of it can be found in German Patent Disclosure DE 4436 465 A1.

To explain the function of the invention in further detail withreference to FIG. 6, the following variables will be presented: U_(HBMP)designates the voltage at the half bridge center point. Because of theonly slight voltage drop at the discharge diode D11, U_(HBMP) isapproximately equal to the voltage U_(C11), to which the positivefeedback capacitor C11 is charged. A voltage of 230 V_(DC) is applied tothe positive pole of the circuit. Because in the exemplary embodimentthe highest possible value for U_(HBMP) is 230 V and because of the lowimpedance of the main switch transistors T1 and T2 that are switched onin alternation, U_(HBMP) is the first guide variable for the discussionbelow.

The second guide variable is the current I_(MP) through the primarywinding of the power transformer LÜ. This variable I_(MP), because ofits wide amplitude and because W=(L/2)*I², has the greatest alternatingenergy content in the arrangement of FIG. 5. All the other currents inthis arrangement, except for I_(L1), are dependent directly orindirectly on I_(MP). The voltages across C_(K1) and C_(K2) add up to230 V and are established such that I_(MP) is purely an alternatingcurrent. If the main switch T1 conducts in the positive direction, thenI_(CT1)=I_(MP).

On the assumption that the magnetizing inductance of the triggertransformer STR is inoperative at the switching frequencies involved,the fraction of the main current I_(MP), as defined by the winding ratioof the control transformer STR, is transmitted precisely to its “lowersecondary winding” as the current I_(STR1), as long as the main switchT1 is capable of conduction. The direction of winding in the controltransformers STR results first in the positive feedback of current andsecond in the push-pull mode, that is, turning on T1 and T2 inalternation. It follows from this that whenever T2 is to be turned on,the same fraction of I_(MP) as just described is transmitted as I_(str2)to the “upper secondary winding”.

The contribution that I_(str1) contributes to triggering T1 is reducedby the applicable value of I_(L1) flowing in the oscillation reversalcoil L1. As long as I_(CT11)=0, and as long as U_(HBMP) isintermittently constant, the following equation applies:

I_(BT1)=I_(str1)−I_(L1).

In the other phases, that is, during the switchover events, that is,while U_(HBMP) is varying over time, the trigger current I_(BT1) for themain switch T1 is reduced by the auxiliary switch collector currentI_(CT11) and is raised by the base bridge capacitor current I_(CBB). Theequation that applies is then:

I_(BT1)=I_(str1)−I_(L1)+I_(CBB)−I_(CT11).

Since the oscillation reversal coil L1 is connected directly parallel tothe base-to-emitter path of the main switch T1, the third independentvariable I_(L1) is determined solely by the inductance of theoscillation reversal coil L1 and by the main switch control voltageU_(BT1). As long as T1 is triggered, or in other words U_(BT1) ispositive, I_(L1) rises in ramplike fashion. As long as T2 is triggered,because of the direction of winding in the triggering transformer STR,the control voltage of the upper main switch is inverse on the lowerside; U_(BT1) is negative, and I_(L1) decreases in ramplike fashion.This produces the triangular course of I_(L1).

In contrast to DE 44 36 465 A1, the oscillation reversal coil L1 isconnected here directly to ground. The essential function of thiscomponent remains unaffected by this.

If U_(HBMP) varies over time, then U_(C11) is changed accordingly.Because of the capacitor C11, the charge current I_(C11) is obtained,which at positive values in the counting direction flows in the form ofI_(BT11) through the base of the auxiliary switch T11 and turns it on;at negative values, it flows as I_(D11) through the discharge diode D11.

The voltage of the base of the transistor T11 compared to the referencepotential, that is, the trigger voltage for the auxiliary switch T11, isU_(BT11). With reference to FIG. 6, the course over time of thevariables thus introduced is as follows:

FIG. 6a first shows the ongoing change in the voltage U_(HBMP) betweenground and an applied direct voltage. It should be noted that the edgesof the voltage course of U_(HBMP) have a finite rise or fall time thatis other than zero.

FIG. 6b shows the current course I_(MP), which fluctuates about the zeropoint and is sometimes positive and sometimes negative. Because of itscoupling in the control transformer STR, the current I_(str1)corresponds to the course of the current I_(MP). The current I_(L1) hasa substantially nearly triangular course.

Since

I_(BT1)=I_(str1)−I_(L1),

it follows that I_(BT1) becomes negative as soon as it is true thatI_(L1)>I_(str1). At those times, the carriers in the base-emitter diodeof the transistor T1 are actively removed, and a fast switch-off eventof the transistor T1 is therefore prepared for.

The course of the current I_(C11) through the capacitor C11, shown inFIG. 6c, is composed of positive pulses and negative pulses. Thepositive pulses occur during the leading edges of the voltage U_(HBMP)and are carried as current I_(BT11) to the base of the auxiliarytransistor T11. After a positive pulse of this kind, the positivefeedback capacitor C11 is in the charged state. The negative pulsesoriginate in the voltage U_(HBMP) that decreases during the transitionof the transistor T1 from the OFF state to the ON state; this voltage isthe source of the discharge current that flows through the diode D11 tothe capacitor C11. As a result, the capacitor C11 is discharged and isagain available for positive feedback during the next turn-on event ofthe transistor T1.

FIG. 6d shows the course of the voltage U_(BT11), which corresponds tothe base-to-emitter voltage at the transistor T11. The positive pulsescorrespond to the base-to-emitter voltage of the transistor T11 in itsON state, while the negative pulses correspond to the voltage droppingat the diode D11 when this diode is in its conducting state.

What is claimed is:
 1. A circuit arrangement, having at least oneelectric main switch (T1; T2) with a reference electrode (E), a controlelectrode (B), and a work electrode (C), a free-wheeling diode (D1; D2),which is connected antiparallel to the main flow direction of each mainswitch (T1; T2), characterized in that each main switch (T1; T2) isassigned an electric auxiliary switch (T11; T22), whose work electrodeis connected to the control electrode (B) of the associated main switch(T1; T2) and whose reference electrode is connected to the referenceelectrode (E) of the associated main switch (T1; T2), and at least onecapacitor (C11; C22) is disposed between the control electrode of theauxiliary switch (T11; T22) and the work electrode (C) of the associatedmain switch (T1; T2), and a discharge unit (E11; D11; D22) is disposedbetween the control electrode and the reference electrode of theauxiliary switch in such a way that the at least one capacitor (C11;C22) can be discharged during the transition of the main switch (T1; T2)from the OFF state to the ON state.
 2. The circuit arrangement of claim1, characterized in that the discharge unit (E11) includes a resistor.3. The circuit arrangement of claim 1, characterized in that a mainswitch (T1; T2) is a bipolar transistor.
 4. The circuit arrangement ofclaim 1, characterized in that a main switch (T1; T2) together with theassociated free-wheeling diode (D1; D2) is realized by a MOSFET.
 5. Thecircuit arrangement of claim 1, characterized in that the discharge unit(E11) has a sense output terminal, which is connected to the controlelectrode of the auxiliary switch (T11) such that the switching statusof the main switch and/or the auxiliary switch can be interrogated viathe sense output terminal.
 6. The circuit arrangement of claim 5,characterized in that at least one capacitor (C_(S11)) is disposedbetween the sense output terminal and the control electrode of theauxiliary switch (T11).
 7. The circuit arrangement of claim 1,characterized in that an auxiliary switch (T11; T22) is a bipolartransistor, a bipolar transistor with a series diode in the collector, aMOSFET, or a MOSFET with a series diode in the drain, and if a seriesdiode is used, its orientation is made such that a current flow in themain flow direction of the associated auxiliary switch (T11; T22) ismade possible.
 8. The circuit arrangement of claim 7, characterized inthat the series diode of the auxiliary switch (T11; T22) is a p-n orSchottky diode.
 9. The circuit arrangement of claim 1, characterized inthat the discharge unit has a shut-down input terminal (SD), by way ofwhich a signal that switches the auxiliary switch (T11) to the ON statecan be applied.
 10. The circuit arrangement of claim 9, characterized inthat the shut-down input terminal (SD) is connected to the controlelectrode of the auxiliary switch (T11), and between the shut-down inputterminal (SD) and the control electrode of the auxiliary switch (T11), aswitch-off diode (D_(SD)) is disposed, whose cathode is connected to theterminal of the control electrode of the auxiliary switch.
 11. Thecircuit arrangement of claim 10, characterized in that the switch-offdiode (D_(SD)) is a p-n or Schottky diode.
 12. A bridge circuit havingat least one first and one second circuit arrangement (10 a, 10 b) ofclaim 1, characterized in that by the first and second circuitarrangements (10 a, 10 b), a bridge is formed in that the referenceelectrode of the main switch (T2) of the second circuit arrangement (10b) is connected to the work electrode of the main switch (T1) of thefirst circuit arrangement (10 a).
 13. A self-oscillating oscillatorcircuit for operating a load, having a bridge circuit of claim 12,characterized in that it has a switching control device (STR) forfeedback transmission of the load current (I_(MP)) to the controlelectrodes of the main switches (T2, T1) of the first and second circuitarrangements (10 b, 10 a), and the control electrode of each main switch(T1; T2) is connected by a respective terminal line to the switchingcontrol device (STR).
 14. The circuit of claim 13, characterized in thatthe switching control device is a control transformer (STR).
 15. Thecircuit of claim 13, characterized in that the two terminal lines areconnected in turn to one another via at least one base bridge capacitor(C_(BB)) and that the base bridge capacitor (C_(BB)) is connecteddirectly to the control electrode of each main switch (T1; T2) and/ordirectly to the output of the switching control device (STR) orientedtoward the control electrode of the applicable main switch (T1; T2). 16.The circuit arrangement of claim 1, characterized in that the dischargeunit (E11) includes a discharge diode (D11; D22).
 17. The circuitarrangement of claim 16, characterized in that at least one resistor isconnected in series with the discharge diode (D11; D22).
 18. The circuitarrangement of claim 16, characterized in that the discharge diode (D11;D22) is a Schottky diode, a Zener diode or a p-n diode.
 19. The circuitarrangement of claim 16, characterized in that at least one resistor isconnected in parallel with the discharge diode.
 20. The circuitarrangement of claim 16, characterized in that at least one resistor isconnected in series with the discharge diode and at least one resistoris connected in parallel with the discharge diode.
 21. The circuitarrangement of claim 1, characterized in that it also has anantisaturation unit (A11), which is disposed between the work electrodeand the control electrode of the auxiliary switch (T11) and whichprevents saturation of the control electrode of the auxiliary switch(T11).
 22. The circuit arrangement of claim 21, characterized in thatthe antisaturation unit (A11) has an antisaturation resistor, which isdisposed such that in the event of saturation of the control electrodeof the auxiliary switch (T11), charge carriers can flow away to the workelectrode of the auxiliary switch.
 23. The circuit arrangement of claim21, characterized in that the antisaturation unit (A11) has anantisaturation diode, which is disposed such that in the event ofsaturation of the control electrode of the auxiliary switch (T11),charge carriers can flow away to the work electrode of the auxiliaryswitch.
 24. The circuit arrangement of claim 23, characterized in thatthe antisaturation diode is a p-n or Schottky diode.
 25. The circuitarrangement of claim 23, characterized in that at least one resistor isconnected in series with the antisaturation diode.
 26. The circuitarrangement of claim 23, characterized in that at least one resistor isconnected in parallel with the antisaturation diode.
 27. The circuitarrangement of claim 23, characterized in that at least one resistor isconnected in series with the antisaturation diode and at least oneresistor is connected in parallel with the antisaturation diode.